1. Field of the Invention
The present invention generally relates to wireless mobile communications network like cellular telephony networks (particularly, although not limitatively, second-generation networks like GSM—General System for Mobile communications—networks and third-generation networks like UMTS—Universal Mobile Telecommunications System—networks, and equivalent standards).
2. Description of the Related Art
A wireless mobile communications network needs from time to time to be upgraded for meeting changing coverage and handled traffic demands. This also applies to relatively mature networks like GSM networks.
The need of upgrading a wireless mobile communications network may for example derive from the necessity of eliminating geographic areas that are subject to excessive interference, so as to achieve a better quality of service, tracking the changing distribution on the territory of the users, ensuring the coverage of geographic areas that are still uncovered (ensuring in particular adequate signal coverage in indoor, in-car, outdoor conditions).
Upgrading a wireless mobile communications network involves planning the changes to be made to the network's cells parameters before deploying the upgrades.
Several network planning tools are known in the art, which are used by network designer for planning wireless mobile communications networks before their deployment on the field.
Generally, the goal of the network planning is ensuring that radio resources are available (with a satisfactory quality of service) in respect of a set of network services in a target geographic area. This goal is reached if, in each area element (pixel) of the target area the generic mobile terminal receives network's common channels signals with a sufficient quality (this being a precondition for allowing the mobile terminal perceiving the presence of the network and selecting the network cell to attach to), the signals transmitted in uplink by the mobile terminal are received with a sufficient quality by the transceiver stations of the network, and the signals transmitted in downlink by the transceiver stations of the network are received with a sufficient quality by the mobile terminal.
Different indicators may be used to assess the above conditions, depending on the network type. For example, in the case of a GSM network, an indicator is the electric field value (or the received signal strength) in the generic pixel of the target area, and the signal-to-noise ratio (C/I). In the case of a UMTS network, which as known exploits a Code Division Multiple Access (CDMA) modulation technique, indicators similar to those exploited for a GSM network are used for signaling channels (like the Common Pilot Channel—CPICH—, a channel that is not subjected to power control), but further considerations are made for taking into account the aspects of macrodiversity (i.e. the possibility that a mobile terminal is simultaneously connected to several transceiver stations) and power control in uplink and downlink. Another peculiarity of UMTS networks is that while in a GSM network the network capacity per transceiver station is fixed a priori (depending on the number of radio carriers assigned to the transceiver station), this is not true for a UMTS network, wherein the capacity depends, in addition to the radio resources assigned to the generic transceiver station, also on the peculiar signal propagation and interference that are experienced in a network cell; for this reason, the network capacity analysis is performed contextually to the analysis of the interference and signal power.
In the planning of the network before its deployment, a-knowledge of the actual traffic handled by the network in the target area is by definition missing; the network planning may thus be made under the assumption of zero handled traffic. This may be a problem for networks like UMTS networks, in which, as discussed above, the aspects of the interference are closely related to the handled traffic. For this reason, a tuning or re-planning of the network parameters is necessary after the network has been deployed on the field.
Generally, the network re-planning involves having the network manager running a “drive test” to collect measures from the deployed network useful to identify areas where the deployed network exhibits criticalities (for example, an area where calls drops occurs due to absence of network signal or pilot pollution—a phenomenon taking place when the number of different transceiver station signals received in a generic pixel with a strength above the macrodiversity threshold, and for which the Ec/Io (energy to noise and interference ratio) of the CPICH is higher than a predetermined threshold, exceeds the maximum number of transceiver stations to which the generic mobile terminal can connect in macrodiversity). Using the collected measures, the network manager performs a network simulation conducted exploiting an automated network planning tool; if the results of the simulation evidence similar criticalities as those evidenced by the measures collected by means of the drive test, the network manager, using the network planning tool, examines possible changes to be made to the deployed network, evaluating the effects thereof on the global network performance (not only in the critical areas). The network manager then selects the change that represents a good trade-off in terms of costs-benefits, and the deployed network is modified accordingly. Then, running a new drive test, the effectiveness of the changes is evaluated.
WO 02/11478 discloses a system for monitoring the performances of mobile telephony networks. In a system for checking performance quality of mobile telephony networks, specific electronic devices are connected to digital data transmission lines between base stations controllers (BSCs) and base transmitting stations (BTSs) dedicated to peripheral areas, or cells, such devices being apt to acquisition of data transmitted onto said lines and to process said data for identification of specific network operating parameters and for correlation of said parameter between them. The above electronic devices are also connected to central processing units where the above processed data are periodically transmitted to for later searching and processing according to design and network maintenance requirements, or any other requirement of users connected by means of remote terminals to said central units. In particular, the hardware of the system allows extracting from the interface between the BTSs and the BSCs network messages formed by a message part related to the type of event characterizing the measure, for example channel request or measurement ratio, and by another message part carrying service parameters like the electromagnetic field level, the distance from the BTS, the quality of service. The software of the system allows arranging the measures in such a way as to build tables of statistical indicators by correlating various available data (e.g., the electromagnetic field level and the quality of service). The data can be correlated in different ways, depending on the estimations needed by the network planner, who may have to face problems of network's expansion or maintenance of the deployed network.
U.S. Pat. No. 6,522,888 discloses a system for determining wireless coverage using location information for a wireless unit. The disclosed system uses location information for a wireless unit and collects information on communications between the wireless unit and the wireless communications system in association with the location information. The wireless communications system determines and/or receives location information for the wireless unit along with other information associated with the location information. The information by location can be used to represent the coverage of a geographic region. For example, during communications between a serving base station and a wireless unit, the serving base station could receive and/or determine signal quality measurements of a forward link and/or of a reverse link at a particular location. Additionally, neighboring base stations can monitor the communications and determine and/or receive location information for the location of the wireless unit along with the information associated with or corresponding to the location of the wireless unit. The associated information can be linked with additional parameters, such as wireless unit type, wireless unit identity, frequency, operating conditions and/or base station identity.